A US man accused of a scheme to rob people who replied to a job ad on Craigslist has been charged with aggravated murder, kidnapping and robbery in the killing of three men and could face the death penalty if convicted, according to an indictment announced on Friday.

Richard Beasley, 52, has denied involvement in the plot, which lured single and older out-of-work men to a non-existent farm in rural Ohio. A fourth man was wounded in the series of attacks last autumn.

Prosecutors would not speculate on a motive, but attorney general Mike DeWine said investigators are looking at "serial killings."

"Are there more bodies? We, frankly, do not know," DeWine said.

Beasley has been jailed on unrelated prostitution and drug charges. He was arrested in November after authorities linked him to the alleged plot. A message was left with the attorney who has been representing him on the non-Craigslist charges.

An acquaintance of Beasley, 16-year-old Brogan Rafferty, could face similar charges after being transferred to adult court late last year.

Authorities say the scheme targeted men with backgrounds that made it unlikely their disappearances would be noted right away.

The first victim, Ralph Geiger, 55, was killed the day after he left a homeless shelter saying he was taking a farm job. His body wasn't found until November 25.

The second victim, David Pauley, 51, came to Ohio after answering the Craigslist ad. A friend has said Pauley was desperate for work. Police say he was killed October 23, and his body was found November 15.

The third victim, Timothy Kern, 47, answered the ad and was last seen November 13, authorities said. His body was also found November 25.

A surviving victim, Scott Davis, 48, answered the ad and was shot on November 6 before escaping, police say.

Geiger's brother, Mark Geiger, said Friday he is not a death penalty advocate but wouldn't oppose it, although life in prison for Beasley would also satisfy him.

"As long as Beasley never has the opportunity to interact with the outside world again, that's what I feel would be appropriate," Geiger said.

Beasley was a Texas parolee when he returned to Ohio in 2004 after serving several years in prison on a burglary conviction. He was released from jail in July after a judge mistakenly allowed him to post bond on a drug-trafficking charge.

In a four-page handwritten letter to the Akron Beacon Journal newspaper, Beasley has said he has been miscast as a conman when he really helped feed, house and counsel scores of needy families, alcoholics, drug addicts, the mentally ill and crime suspects for years.

"To call me a conman when I sacrificed for others is wrong," wrote Beasley, who didn't mention the Craigslist investigation. "To turn their back on me is not following Christ's example."